湘东宏夏桥和板杉铺岩体LA-MC-ICPMS锆石U-Pb年龄及地质意义  

LA-MC-ICPMS Zircon U-Pb Geochronology of the Hongxiaqiao and Banshanpu Granitoids in Eastern Hunan Province and Its Geological Implications

作　　者：李建华[1] 张岳桥[1] 董树文[1] 马之力[1,2] 李勇[1] 

机构地区：[1]中国地质科学院地质力学研究所,北京100081 [2]合肥工业大学资源与环境科学系,安徽合肥230009

出　　处：《地球学报》2015年第2期187-196,共10页Acta Geoscientica Sinica

基　　金：中国地质科学院地质力学研究所基本科研业务费项目(编号:DZLXJK201403);中国地质调查局地质调查项目"华南深部结构探测"(编号:12120114067801);国家专项"深部探测技术与实验研究"(编号:Sino Probe-08-01)联合资助

摘　　要：运用阴极发光技术，对湖南东部宏夏桥和板杉铺岩体的锆石进行了内部结构分析，在此基础上利用LA-MC—ICPMS锆石U-Pb定年方法进行了同位素年代学测定。结果显示，宏夏桥2个黑云母花岗闪长岩样品分别给出了（421±2）Ma和（423±2）Ma的主体谐和年龄；板杉铺2个黑云母二长花岗岩样品给出了（422±2）Ma和（421±2）Ma的谐和年龄。这两岩体均为准铝质一过铝质花岗岩，具明显高Sr／Y和La／Yb比值和负硝d（力值，与埃达克岩类似，推测它们为早古生代华南地壳缩短加厚和部分熔融作用的产物。综合区域岩浆和变形变质年龄，本文认为，华南早古生代陆内挤压造山作用发生于～460～420Ma，以前泥盆纪地层广泛褶皱和大规模地壳重熔型岩浆活动、混合岩化作用、基底韧性剪切及高级变质作用为主；陆内造山后期的伸展松弛作用发生于～420～385Ma，主要表现为后造山花岗岩形成、张扭性韧性剪切和退变质作用。Internal structures and crystallization ages of zircons from the Hongxiaqiao and Bashanpu granitoids were analyzed using the CL technology and the LA-MC-ICPMS zircon U-Pb method, and the results show that the Hongxiaqiao granodiorite and Banshanpu monzonitic granite yield U-Pb zircon ages of 423-421 Ma and 422-421 Ma, respectively. Reliable geochemical data suggest that the two granitoids are metaluminous to peraluminous and share geochemical characteristics of typical adakitic rock, as expressed by high Sr/Y and La/Yb ratios and negative εNd（t） ratios, implying that they might have originated from partial melting of the thickened crust of South China during the Early Paleozoic period. Our geochronoglcial data, coupled with available isotopic ages related to regional rnagmatism and metamorphism, suggest that two stages of tectono-thermal events feature the Early Paleozoic intracontinental orogeny within South China. The earlier compressional event occurred at ca. 460-420 Ma and was characterized by widespread folding of pre-Devonian strata, crustal thickening and anatexis, migmatization and high-grade metamorphism. The later extensional event occurred at ca. 420-385 Ma and was characterized by the generation of post-orogenic granites as well as locally distributed transitional shearing and retrograde metamorphism.

关 键 词：宏夏桥 板杉铺 锆石U-PB 华南 古生代 陆内造山 

分 类 号：P597[天文地球—地球化学] P588.121[天文地球—地质学]